The present invention is directed to integrated circuits. More particularly, the invention provides amplification systems and methods with one or more channels. Merely by way of example, the invention has been applied to a Class-D amplifier. But it would be recognized that the invention has a much broader range of applicability.
FIG. 1 is a simplified conventional diagram showing an amplification system using a Class-D amplifier with one channel. The amplification system 100 includes a modulator 102, an output stage 104, a low-pass filter 106, and an output load 116. The modulator 102 includes an oscillator 108, a comparator 110 and a loop filter 112. For example, the output load 116 is a speaker. In another example, the modulator 102, the output stage 104, and the low-pass filter 106 are included in a Class-D amplifier. In yet another example, the low-pass filter 106 includes one or more inductors and/or one or more capacitors. In yet another example, the low-pass filter 106 includes one or more bead cores and/or one or more capacitors.
The loop filter 112 receives an input audio signal 118 and an output signal 120 (e.g., a pulse-width-modulation signal) and outputs a filtered signal 122 to the comparator 110. For example, the input audio signal 118 includes a pair of input signals. The oscillator 108 generates a clock signal 126 and a ramp signal 124 which is received by the comparator 110. The comparator 110 outputs a comparison signal 128 that indicates a comparison between the ramp signal 124 and the filtered signal 122. The output stage 104 receives the comparison signal 128 and generates the output signal 120. The low-pass filter 106 converts the output signal 120 to an audio signal 130 to drive the load 116. As shown in FIG. 1, one channel including the modulator 102 and the output stage 104 is implemented. Multiple channels may be used for audio-amplification applications.
In one embodiment, the loop filter 112 amplifies an error signal between the input signal 118 and a feedback signal associated with the output signal 120. For example, the loop filter 112 includes a low pass filter which has a very high gain (e.g., a high gain larger than 1000) in a low frequency range and a very low gain (e.g., a low gain much smaller than 1) in a high frequency range. In another example, if a signal includes a low-frequency component and a high-frequency component, the loop filter 112 amplifies the low-frequency component with a high gain and amplifies the high-frequency component with a low gain (e.g., a low gain much smaller than 1). In yet another example, if the high-frequency component is close to a switching frequency of the amplification system 100, the loop filter 112 attenuates the high-frequency component. In one embodiment, the loop filter 112 includes one or more stages of analog integrators.
FIG. 2 is a simplified conventional diagram for an amplification system with multiple channels. The amplification system 300 includes multiple channels 2021, . . . , 202n, . . . , 202N, where N≧2 and 1≦n≦N. The first channel 2021 includes a loop filter 2041, comparators 2061 and 2081, a logic controller 2101, driving components 2121 and 2141, transistors 2161, 2181, 2201 and 2221, and a low-pass filter 2241. The logic controller 2101 includes one or more buffers. For example, the low-pass filter 2241 includes one or more inductors and/or one or more capacitors. In another example, the low-pass filter 2241 includes one or more bead cores and/or one or more capacitors. Other channels have similar components as the first channel. As shown in FIG. 2, these channels 2021, . . . , 202n, . . . , 202N share a common ramp signal 228 and generate output signals (e.g., 2341, . . . , 234n, 234N and/or 2361, . . . , 236n, . . . , 236N) so that audio signals are provided to output loads 2221, . . . , 222n, . . . , 222N (e.g., speakers) respectively.
In one embodiment, the loop filter 2041 amplifies the error signal between an input differential signal and a feedback differential signal associated with an output differential signal. The input differential signal represents a difference between the input signals 2301 and 2321, and the output differential signal represents a difference between the output signals 2341 and 2361. For example, the loop filter 2041 is a low pass filter and it has a very high gain (e.g., a high gain that is greater than 1000) in a low frequency range and a very low gain (e.g., a low gain that is much smaller than 1) in a high frequency range. In another example, if a signal includes a low-frequency component and a high-frequency component, the loop filter 2041 amplifies the low-frequency component with a high gain and amplifies the high-frequency component with a low gain (e.g., a low gain that is much smaller than 1). In yet another example, if the high-frequency component is close to a switching frequency of the amplification system 200, the loop filter 2041 attenuates the high-frequency component. In one embodiment, the loop filter 2041 includes one or more stages of analog integrators. In some embodiments, loop filters in other channels are the same as the loop filter 2041.
The amplification systems 100 and 200 often have certain disadvantages. Hence it is highly desirable to improve such amplification systems.